The computer as seen by Chibo engineers

A PC consists of the assembly of electronic components, having various functions, metal structures and plastic material. Schematically, four main parts can be identified:

1. central unit

2. monitor

3. keyboard

4. peripherals

Central Unit

The Central Unit consists of printed circuit boards and plates consisting of a plastic substrate onto which integrated circuits, capacitors, resistors, and inductors are attached. All these elements are properly connected to each other by tracks of conductive alloy material deposited on the plate.

Printed circuit boards

In the manufacture of printed circuit boards and plates, the main raw materials used are:

• thermoset resin-based polymer laminates reinforced with glass fibers (usually epoxy or phenolic, sometimes also polyester, melamine, etc.);

• screen printing inks and pastes;

• photopolymers (polyester-based, acrylic-based, etc.);

• inorganic and organic chemical compounds for the filler and removal steps by electrochemical processes and for photopolymer and copper removal;

• protective paints;

• fixatives and thinners;

• precious and non-precious metals.

A printed circuit board, on the other hand, consists of:

• 33% ceramic and glass in the components and packaging, reinforcements of PWBs (Printing Wiring Boards);

• 33% plastics in PWBs, components and packaging, connectors;

• < 1% paper and liquids in capacitors;

• 33% metals in component conductors, PWB tracks.

In addition, there are also metals distributed as follows:

• 12% copper (component conductors, PWB tracks, connectors);

• 7% iron (component conductors, mechanical details, inductors);

• 2% nickel (component parts and component conductors);

• < 1% zinc (surface treatments);

• < 1% tin (solder);

• 1% lead (solder);

• < 1% manganese (electronic dry capacitors);

• < 1% antimony (component soldering and assemblies);

• < 8% other metals (chromium, titanium, tungsten, silver, palladium, aluminum, barium, boron, beryllium, cobalt, etc.).

Integrated circuits

Integrated circuits consist of a matrix of semiconductor material, usually silicon, encapsulated in an enclosure that may be ceramic or plastic material and metal conductors for connection with other components. The plastic casing is the most common type for integrated circuits today, accounting for more than 90 percent of all integrated circuit casings.

Plastic casing generally has the following composition:

• 65-75% inert filler, usually silicate, SiO2;

• epoxy resin 20-30%;

• flame retardant 2-6% consisting of antimony oxide Sb2O3;

• curing agent 1-10%, usually an amine hardener

• (5-30% of total resin weight);

• accelerator 0.6-1% consisting of a Lewis acid, e.g., boron trifluoride, in the form of its monoethylamine complex (about 3% of the weight of the resin);

• dye 0.5% usually consisting of carbon black;

• compound release agent usually natural wax or carnauba wax.

Leadframe

The leadframe consists of silicon, with small concentrations of bromine, phosphorus, arsenic, and antimony, and is covered with a very small layer of aluminum, about 0.001 mm, sometimes also with plastic or ceramic to protect it.

The chip's connections to the leadframe are usually made of alumina, with added oxides of magnesium, calcium, silicon, and titanium. Other semiconductor materials generally used are germanium, gallium arsenide, gallium phosphide, indium phosphide, and gallium arsenide/gallium phosphide. Germanium is used for diodes and other materials, generally for LEDs. Diodes are generally made using germanium and silicon.

Capacitors

There are several types of capacitors, characterized by different dielectric materials. The most commonly used capacitors are:

• metallized paper capacitors consisting of two strips of cellulose, metallized on one side with a thin film of zinc or other low melting point metal; they also contain paper, zinc, lead, tin, iron and copper;

• metallized plastic capacitors, with the same composition as the previous ones, may contain polycarbonate and polypropylene;

• aluminum electrolytic capacitors, contain boric acid, mixed with glycol, salts and organic solvent, the latter may be butyrolactone, dimethylformamide or dimethylacetamide, as the electrolyte. Other substances that can be used in this regard are methylpyrrolidone, ethylene glycol, adipic acid, nitrophenol, and organic amine compounds;

• tantalum electrolytic capacitors, operate through the same principle as aluminum electrolytic capacitors and use Ta2O5 as the dielectric layer and manganese dioxide, as the electrolyte.

Resistors

They consist of an alumina ceramic substrate on which a layer of conductive metal or glass-carbon mixture is deposited. The terminals are usually gold, palladium-silver, or materials having the same electrical properties.

Inductors

These consist of a winding of copper wire around a ceramic or ferromagnetic core. The inductor can, then, be coated with epoxy resin. The ferromagnetic core may be made of iron sintered with organic binders, Fe-Ni or Fe- Zn alloy, and may contain Sm, Pr, Co or Nd.

Relays

Relays are used with peripheral control functions and are characterized by low current loss, low sensitivity to external disturbances and high reliability.

The most common materials used in relays are iron, copper and epoxy resins. The properties of copper spring contacts are generally improved by the use of beryllium. Fe, Ni, Mn, Zn, Co, Cr, Si, Mo, Ti, C, V, Ba, Sm, Sr, Se, Pr, and Nd are used in magnetic parts. A high-performance core often contains Fe combined with Sm, Nd or Co.

Welds and adhesives

Solder is generally made from alloys consisting of 63% tin and 37% lead. For SMT (Surface Mount Technology) alloys of 2% silver, 36% lead, and 62% tin are commonly used. However, the total use of silver is modest as only 10% of electronic components use SMT solder. Other solder materials include antimony-tin, bismuth-tin, and indium-tin alloys. The most commonly used adhesives are usually compounds of epoxy or acrylic nature.

Printed Wiring Board (PWB)

There are two major groups of PWBs with and without reinforcement. PWBs without reinforcement can be flexible or rigid types. The most common types of reinforcement are glass and cellulose paper wefts. The resins used for PWBs with reinforcement generally contain brominated flame retardants.

Indicator lights

Indicator lights generally consist of LEDs. These contain small amounts of semiconductor materials consisting of InP or GaP.

Enclosure

The casing of the data processing unit is made of metal with plastic parts (about 300 g).

Monitors

Computer equipment monitors also contain printed circuit boards with a total area of 500 cm2, as well as cathode ray tube and display.

Cathode Ray Tube

A cathode ray tube essentially consists of four parts: the cone part, the screen, the connection between the cone and the screen, and the electronic part.

The glass used in the manufacture of cathode ray tubes can be of different types, but all contain metal oxides capable of absorbing rays (PbO, BaO, SrO). The fluorescent substances contained within the screen are usually sulfides or phosphides of zinc, europium, yttrium, and cadmium.

In older models the fluorescent coating contains mainly cadmium and zinc sulfides, while in newer models it is 94% zinc sulfide and rare earths.

Displays

There are different types of displays:

• liquid crystal displays which use 2000 different types of liquids, including trans-4-propyl-(4-cyanophenyl)-cyclohexane and azoxybenzene, while, the lamp to backlight the screen generally contains mercury or other rare metals;

• plasma displays contain mercury or radioactive isotopes such as Ni63, Kr85 or H3;

• electroluminescent displays are generally ZnS-based compounds and heavy metals or rare earth group metals.

Enclosure

The monitor casing is made of ABS plastic or similar containing about 20% flame retardant (deca or octa-BDE) and has a weight of about 1.7 kg.

Keyboard

It consists mainly of printed circuit boards covering an area of about 200 cm2 and the plastic cover.

In conclusion, the main materials that make up a computer can basically be grouped as follows:

MATERIAL WEIGHT (kg) %

Ferrous metals 7.5 32

Nonferrous metals 0.5 2

Glass 3.6 15

Plastic 5.2 22

Printed circuit boards (PCBs) 5.3 23

Disk drivers 1.2 5

Total 23.3 100